An apparatus for measuring changes in microwave frequencies corresponding to the density of a fluid

ABSTRACT

An apparatus for measuring the density of a dielectric fluid retained in a vessel. A waveguide is inserted into the liquid through a sealed opening in the vessel. The waveguide has a center conductor concentrically positioned in the waveguide. The center conductor carries a microwave frequency emitted from a source to a disc on the bottom of the waveguide where a fixed node of the microwave frequency occurs. A detector member immersed in the fluid is fixed to the waveguide a predetermined distance from the bottom of the waveguide to receive a node of the standing wave created by the microwave frequency. With a change in the fluid density, the node adjacent the detector member will correspondingly shift with the detector member receiving a different electromagnetic field intensity created by a microwave energy source transmitted through the waveguide. The detector member will communicate all measurements of the electromagnetic field intensity to an indicator where density changes can be directly read from a scale.

United States Patent inventor Aloysius Bak Primary Examiner-Edward E.Kubasiewicz Davenpofl, 10W! Atrorneys- Plante, Arens, Hartz, Hix & Smithand William N. [21] Appl. No. 848,240 Antonis [22] Filed Aug. 7, 1969[45] Patented Dec. 7, 1971 [73] Assignee The Bendix CorporationABSTRACT: An apparatus for measuring the density of a dielectric fluidretained in a vessel. A waveguide is inserted into the liquid through asealed opening in the vessel, The waveguide has a center conductorconcentrically positioned in the waveguide. The center conductor carriesa microwave [54] APPARATUS FOR MEASURING CHANGES IN frequency emittedfrom a source to a disc on the bottom of the MICROWAVE FREQUENCIESCORRESPONDING To THE DENSTY OF A FLU") waveguide where a fixed node ofthe microwave frequency oc- 3 Claims 3 Damn Fi curs. A detector memberimmersed in the fluid is fixed to the g waveguide a predetermineddistance from the bottom of the [52] [1.8. CI 324/58.S B waveguide toreceive a node of the standing wave created by [51] Int. Cl G0lr 27/04the microwave frequency. With a change in the fluid density, [50} Fieldof Search 324/58, the node adjacent the detector member willcorrespondingly 58.5; 73/304 shift with the detector member receiving adifferent electromagnetic field intensity created by a microwave energy[56] Refennces Cited source transmitted through the waveguide. Thedetector UNITED STATES PATENTS member will communicate all measurementsof the elec- 3,403,335 9/1968 Couper et al. 324/58 tromagnetic fieldintensity to an indicator where density 3,474,337 10/1969 Petrick324/585 changes can be directly j qmg MKME .svnsr Sol/Cf L6 49 2 r1 v Hl 24 I l 1 l l :1 l l 1. r: I 2 77f I. a?

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32 /8 LLJI \J j A APPARATUS FOR MEASURING CHANGES IN MICROWAVEFREQUENCIES CORRESPONDING TO THE DENSITY OF A FLUID SUMMARY OF THEINVENTION It is an object of this invention to provide an improved fluiddensity indicating system.

Another object of this invention if to provide a fluid densityindicating system having improved sensitivity and accuracy.

A further object of this invention is to provide a fluid densityindicating system employing microwave techniques.

More specifically, it is an object of this invention to provide a fluiddensity indicating system having waveguide means, one end of which isimmersed in said fluid and the other end of which is connected to asource of microwave energy, said system including detector meansconnected to said waveguide means and immersed in said fluid.

Other objects and features of the invention will be apparent from thefollowing description of the fluid density indicating system taken inconnection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view, partially insection, depicting the fluid density indicating system of thisinvention;

FIG. 2 is a sectional view taken along line 22 of FIG. 1; and

FIG. 3 is an enlarged view, partially in section, taken along thelongitudinal axis of the waveguide means to pictorially shown theelectrical operation of the system.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawing,and particularly FIG. 1, a fluid density indicating system is generallyidentified by the numeral 10. The fluid density indicating system iscomprised of a vessel 12 containing a fluid l4, waveguide means 16,shorting means 18, a source of microwave energy 20, and detector means22.

Although the vessel 12 is shown as a generally cylindrically shapedclosed container, other shapes or configurations may, of course, beused. As will be understood by those skilled in the art, the fluid 14must be of a type in which the density is a single-valued function ofthe relative dielectric constant and which is not flammable orcombustible when exposed to the source of microwave energy 20. It isfurther noted that the detector means 22 must be totally immersed in thefluid 14. The source of microwave energy may be selected for anyparticular application and could, of course, be varied from applicationto application. More specifically, the source of microwave energy 20could be comprised of electromagnetic radiation of wavelengths fromsubmillimeter through those greater than 30,000 meters.

The waveguide means 16 is comprised of a plug or guide member 24 whichcarries and vertically positions an outer element 26 of the wave guidemeans 16. As shown best in FIG. 2, the outer element 26 carries an innerelement 28 via a dielectric support 30. As may now be seen by thoseskilled in the art, the outer element 26 and the inner element 28 areconcentrically positioned by the dielectric support 30 to form a coaxialwaveguide of the waveguide means 16. The shorting means 18, being of agenerally disc shape, is attached to the end of the coaxial waveguidewhichis immersed in the fluid I4. The shorting disc or means 18 isstructurally and electrically connected to both the outer element 26 andthe inner element 28 to provide a high-frequency short therebetween. Theouter element 26 is also provided with axial openings or slots 32 ofpredetermined size to allow communication of the fluid 14 into theinterior of the coaxial waveguide 16; i.e., into the space between theinner and outer elements, 28 and 26, respectively.

The other end of the waveguide means 16 has mounted thereto the sourceof microwave energy 20. The source of microwave energy is positioned soas to emit electromagnetic radiation into the coaxial waveguide 16. Themicrowave energy will travel down the coaxial waveguide 16 through themedium above the surface of the fluid (for example air), into the fluid14, past the detector means 22, and through additional fluid 14 until itreaches the shorting means 18 where further travel is precluded by thehigh-frequency short between the inner and outer conductors, 28 and 26,respectively. As will be understood by those skilled in the art, theemission of microwave energy into the coaxial waveguide 16 will producea standing wave 34 which is shown in graphical form in FIG. 3. Thestanding wave 34 may be shown as having voltage amplitude maximums orantinode 36 and minimums or nodes 38 along progressive positions of thecoaxial waveguide 16. The distance between adjacent nodes is determinedby the frequency of the microwave energy and the properties of thefluid. The location of the nodes is determined by the fact that a nodemust exist at the shorting means at all frequencies with any fluid.

The detector means 22 is comprised of an electric field intensitysensitive element 42 and an indicating element 44 electrically connectedby conductors 46 to the field intensity sensitive element 42. Theelectric field intensity sensitive element 42 includes a probe 48 and ismounted to the outer element 26 of the coaxial waveguide 16 such thatthe probe 48 projects through an opening 50 into the interior of thewaveguide 16, as may be best seen in FIG. 3. As clearly seen in FIG. 1,the electric field intensity sensitive element 42, including its probe48, is mounted such that it is fully immersed in the fluid 14. It isimportant to note that the probe 48 must be mounted so that a node 38 ofthe standing wave 34 appears at the exact position of the probe 48 whenthe fluid density reaches one of its extreme values, as shown in FIG. 3for reasons to be more fully explained hereinafter.

Regarding the mode of operation of the fluid density indicating system10, assume that the vessel 12 is filled as shown in FIG. 1, with fluidl4, and that the source of microwave energy 20 is energized, and thusemitting microwave energy. One of the nodes 38 of the standing wave 34will be located at the exact position of the probe 48 so that thepointer 52 of the indicating element 44 is deflected to align with apredetermined numerical indication of the density of the fluid (shown inFIG. 1 as a numeral 10). As the density of the fluid 14 changes, therelative dielectric constant changes and hence the distance betweenadjacent nodes changes. Since the node at the shorting means cannotchange its position, the nodes 38 of the standing wave 34 shift, asshown by the dotted curves in FIG. 3. This shift in the position of thenodes causes the probe 48 and thus the electric field intensitysensitive element 42 to see an increased electric field intensity, whichcauses the indicating element to rotate or move pointer 52 to the leftto indicate a change in fluid density. As will be further understood bythose skilled in the art, the selection of the indicating element 44,the electric field intensity sensitive element 42, the waveguide means16, and the source of microwave energy 20 is such that the pointer 52aligns itself with another predetermined numerical indication of thedensity of the fluid after numerical indication (shown in the drawing asthe numeral to give the indicating system 10 a preselected range ofmeasuring capability.

While the specific details have been herein shown and described, theinvention is not confined thereto, as other substitutions can be madewithin the spirit and scope of the invention.

I claim:

1. An apparatus for directly measuring any change in the density of afluid, comprising:

a vessel for holding a quantity of said fluid;

waveguide means having one end which extends through an orifice in saidvessel and into said fluid, said vessel retaining said waveguide meansin a fixed position in said fluid, said waveguide means having openingstherein to permit said fluid to freely pass to the interior thereof;

means connected to the other end of said waveguide means for emittingmicrowave energy into said waveguide means at a predetermined frequency;

shorting means located in the interior of said waveguide means forcreating a fixed node position for the frequency of the microwaveemitted within said waveguides; and

detector means secured to said waveguide means in said fluid apredetermined distance from said shorting means, said predetermineddistance being selected for the frequency of the microwave to create astanding node adjacent said detector means, said detector meansmeasuring the electromagnetic field created by said microwave energy insaid fluid as a function of said standing node, said standing nodeshifting along the interior of said waveguide means with a change in thefrequency of the emitted microwave energy caused by a variance in thedensity of the fluid in the vessel, said node-shifting creating adifferent electromagnetic field within the interior of ing meansincludes:

a pointer member retained in a housing over a numerical scale, saidpointer member being responsive to the change in electromagnetic fieldintensity measured by said detector to give an operator a visualindication of any fluid density change.

1. An apparatus for directly measuring any change in the density of afluid, comprising: a vessel for holding a quantity of said fluid;waveguide means having one end which extends through an orifice in saidvessel and into said fluid, said vessel retaining said waveguide meansin a fixed position in said fluid, said waveguide means having openingstherein to permit said fluid to freely pass to the interior thereof;means connected to the other end of said waveguide means for emittingmicrowave energy into said waveguide means at a predetermined frequency;shorting means located in the interior of said waveguide means forcreating a fixed node position for the frequency of the microwaveemitted within said waveguide; and detector means secured to saidwaveguide means in said fluid a predetermined distance from saidshorting means, said predetermined distance being selected for thefrequency of the microwave to create a standing node adjacent saiddetector means, said detector means measuring the electromagnetic fieldcreated by said microwave energy in said fluid as a function of saidstanding node, said standing node shifting along the interior of saidwaveguide means with a change in the frequency of the emitted microwaveenergy caused by a variance in the density of the fluid in the vessel,said node-shifting creating a different electromagnetic field within theinterior of said waveguide means, said detector means responding to saidshifting in the standing node to indicate a corresponding change in thedensity of the fluid in the vessel.
 2. The apparatus, as recited inclaim 1, further including: indicating means responsive to said detectormeans for providing evidence of a change in the density of the fluid. 3.The apparatus, as recited in claim 2, wherein said indicating meansincludes: a pointer member retained in a housing over a numerical scale,said pointer member being responsive to the change in electromagneticfield intensity measured by said detector to give an operator a visualindication of any fluid density change.